The present invention concerns a magnetic recording medium for use in magnetic disc apparatus, etc. and, particularly, it relates to a magnetic recording medium of high reliability and high performance suitable for high density recording and having excellent shock resistance, vibration resistance, corrosion resistance and wear resistance.
As magnetic recording media for use in high density recording, those using metallic magnetic thin films or sputtered .gamma.-Fe.sub.2 O.sub.3 thin films have been proposed as described in Japanese Patent Publication Nos. Sho 54-33523 and Sho 57-16732. As Methods for forming films of such media, there have generally been used sputtering, evaporation, ion plating, etc. As the demand for high recording density has increased more and more in recent years, practical use of continuous thin film media using metallic magnetic thin films or sputtered .gamma.-Fe.sub.2 O.sub.3 thin films has begun including those for medium- or small-sized disc apparatus.
For attaining high density recording, it is necessary that the distance between the head and the medium of such a high performance magnetic disc apparatus (head-medium spacing) be decreased to as small as less than 0.3 .mu.m, which increases the risk that the head and the medium are brought into contact upon read and write operation causing error or crushing between the head and the medium. In view of the above, increased shock resistance have been demanded recently and vibration resistance in the disc apparatus, particularly, magnetic disc media for use in high density recording as described above.
Although the wear resistance can be improved by disposing a lubricating non-magnetic overcoat layer on the magnetic film, it is not sufficient for imparting the necessary impact shock resistance and the vibration resistance. Since the covering power, uniformity and adhesion of the non-magnetic overcoat layer are not generally sufficient, if the medium suffers from impact shocks due to disturbance, it is partially destroyed, causes errors and, in an extreme case, undergoes crushing. Furthermore, as compared with the conventional coated medium, the metallic magnetic thin film has a drawback in view of the corrosion resistance, while the sputtered .gamma.-Fe.sub.2 O.sub.3 thin film has a drawback in view of the wear resistance. These drawbacks are caused since the non-magnetic overcoat layers are usually porous and do not substantially function as a corrosion resistance protection layer and since the non-magnetic lubrication layer such as a layer of carbon has extremely poor adhesion to the sputtered .gamma.-Fe.sub.2 O.sub.3 thin film. Thus, the lubrication layer cannot provide sufficient effect.
For the metallic thin film medium, improvement in the corrosion resistance has been attempted by disposing a corrosion resistant protection layer (intermediate layer) composed of Cr with 0.5 .mu." (127 .ANG.) thickness between a Co alloy magnetic layer and a C non-magnetic overcoat layer as shown in the article PS-3, p.13 in the Symposium on Memory and Advances Recording Technologies Text Book, San Jose, Calif., May, 1986. However, according to the study of the inventors, the Cr film of about 100 .ANG. thickness is porous and not uniform and cannot be said to be sufficient as a corrosion resistant protection layer, and no remarkable effect is recognized by the disposition of the Cr layer in view of the wear resistance and the impact shock resistance. Thus, improvement in these characteristics has posed a serious problem. Further, aside from Cr, it has been described in Japanese Patent Laid-Open No. Sho 61-199241 that an improvement can be obtained for the corrosion resistance by disposing an intermediate layer made of noble metal made of one or more of elements selected from among Ag, Au, Pt and Pt and between the protective and lubrication layer and a magnetic layer. However, since the noble metal intermediate layer is soft and poor in the adhesion as compared with Cr, Si, etc., it has been considered unsuitable in view of the wear resistance and impact shock resistance. In addition, these noble metals are expensive bringing about problems for practical use. Separately, while similar structures have been studied also in iron oxide type media, they are considered insufficient in view of wear resistance, impact shock resistance and the vibration resistance, for which further improvements have been demanded.